Scintillation detectors are used in a wide variety of applications, including medical diagnostics and therapy (PET, SPECT, therapy imaging, etc.), oil exploration, field spectrometry, and container and baggage scanning. Desirable properties for scintillation detectors include high light output (i.e., a high efficiency for converting the energy of incident radiation into scintillation photons), efficient detection of the radiation being studied, a high stopping power, good linearity over a wide range of energy, a short rise time for fast timing applications, and a short decay time to reduce detector dead-time and accommodate high event rates. Light output is particularly important, as it affects both the efficiency and resolution of the detector, where efficiency is the ratio of detected particles to the total number of particles impinging upon the detector, and energy resolution is the ratio of the full width at half maximum of a given energy peak to the peak position, usually expressed in percent. The light output is often quantified as a number of scintillation photons produced per MeV of deposited energy.
LSO is a scintillation crystal that is widely used in medical imaging applications, such as for gamma-ray detection in Positron Emission Tomography (PET). LSO is typically doped with 0.05 to 0.5% cerium (Ce), while controlling other impurities at low levels. The light yield of Ce doped LSO (Ce:LSO) crystals grown using prior art methods is on average significantly lower than the theoretical maximum, and the decay time of these crystals tends to be in the 40 ns range. In addition, new techniques for image data acquisition require faster decay times than those obtained with Ce:LSO. Further, scintillation properties of LSO grown under such conditions can vary significantly from boule to boule, and in different parts of the same boule, which consequently increases the cost of commercial crystal production caused by the large number of out-of-spec crystals produced.
Work has been done with codoping the LSO crystals in an attempt to improve the scintillation properties. For example, Ce:LSO has been doped with 0.02% calcium (Ca) or magnesium (Mg). However, although codoping improved light yield some, it failed to change decay time for the crystals.
A need therefore exists for scintillation crystals with improved light yield and light yield uniformity, controllable scintillation decay time that can be optimized for specific applications, and improved decay time uniformity. A need also exists for production techniques with improved yield by reducing the number of out-of-spec crystals produced.